In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk. Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk.
Modern reliability requirements for disk drive systems require each disk to be tested prior to installation in a disk drive system. A portion of this testing is glide testing, where a disk is characterized to determine the maximum height of any non-planar regions, or asperities. This height is known as the glide height for that particular disk. With extremely low flying heights of heads in the modern disk drive systems, it is important to know that a disk does not have asperities greater than a certain height. Disks with glide heights greater than a certain amount can be discarded. This will substantially reduce the number of times a read/write head is struck by a rotating disk in operation, and thus will increase the reliability of disk drive systems.
Typically, a glide height test station is used. The station may include a spindle on to which a disk is placed. The station may also include a head mount block to support a pair of glide heads relative to the disk, with one head proximate to and just above the disk and one head proximate to and just below the disk. The glide heads are generally similar in shape to read/write heads, but do not necessarily include read or write transducers. The primary function of a glide head is to fly close to the surface of the disk and assist in the detection of interference or physical contact with the disk. Typically, this contact is sensed with either an acoustic-emission sensor or a piezoelectric sensor. An acoustic-emission sensor may be provided at the head mounting block or fixture to sense the vibrations of the glide head associated with physical contact with the rotating disk. The piezoelectric sensor is provided in the glide head to supply an electrical signal as a result of the contact with the rotating disk and forces applied throughout the glide head. With either type of sensor, the magnitude of the signal sensed is a function of the disk rotational speed.
It can be appreciated that it is desirable to fly the glide head at the same height for each disk to be tested. With most head designs, however. the fly height is proportional to the disk rotational speed. Since each manufactured glide head will have slightly different surfaces and thus slightly different flying characteristics, it might take a slightly different speed to get each head to an identical height. With two heads in each glide test station, however, give rotational speed for the disk under test may result in two different heights. One approach in the past has been to sort and match-up glide heads to reduce this problem. This approach has many drawbacks such as low yield and the fact that the glide heads are typically sorted by fly height for a given velocity and not by their ability to detect glide height
Another approach has been to design glide heads that have a fly height that is much less dependent on disk rotational speed. In such case, sorting issue described above is greatly minimized but there is another drawback. Many modern glide test protocols test the disk at two different fly heights. With these relatively-fixed fly height heads, positioning the glide head at the two different heights can be difficult.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.